Total knee arthroplasty (“TKA”) is generally performed to replace worn out knee joints with implants. Knee joints, including the patella, wear out over time or may be damaged by ailments such as arthritis. Proper sizing and placement of an implant to replace a damaged patella is crucial in ensuring a successful TKA. Improper implant sizing or poor positioning of the implant may lead to patellar maltracking causing anterior knee pain, increased implant wear, and consequently a higher risk of implant instability leading to patellar fracture. Therefore, ensuring that the natural kinematics of the patella are maintained after the TKA is desired for a successful surgery.
Selecting an implant with the correct thickness is necessary for a successful TKA. Insufficient resection thickness will increase the total height of the patella (with an implant) that will alter the biomechanics of the quadriceps and limit flexion. Whereas, excessive resection may result in a weak resected patella that is prone to patellar fracture. Resection thickness is generally determined based on the total thickness of the patella, which is measured using calipers. However, the irregular morphology of the patella makes it difficult to obtain accurate measurements from a caliper because of the lack of reference points on the patella.
While computer-assisted surgery (“CAS”) procedures are available to assist in determining patella resections, there exists a need to provide a method to generate a patellar coordinate system to properly identify a resection plane and position a properly sized implant thereon.